| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [prep] a [num] year period [prep] | 16 |
|
| 2 | [prep] a [adj] year period [prep] | 16 |
|
| 3 | [prep] a [adj] year period [prep] | 16 |
|
| 4 | over a [adj] year period [prep] | 11 |
|
| 5 | over a [adj] year period [prep] | 11 |
|
